media: siano: Fix error handling in smsdvb_module_init()

The smsdvb_module_init() returns without checking the retval from
smscore_register_hotplug().
If the smscore_register_hotplug() failed, the module failed to install,
leaving the smsdvb_debugfs not unregistered.

Fixes: 3f6b87cf ("[media] siano: allow showing the complete statistics via debugfs")
Cc: stable@vger.kernel.org
Signed-off-by: Yuan Can <yuancan@huawei.com>
Acked-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>